Interlayer tunneling spectroscopy for slightly overdoped Bi₂Sr₂CaCu₂O_8+δ

We have measured the interlayer tunneling characteristics of slightly overdoped Bi₂Sr₂CaCu₂O_8+δ in the c-axis direction from 10 to 220 K by using very thin mesas containing approximately ten CuO₂ double layers. The superconducting gap 2Δ is 50 meV at 10 K and shows a temperature (T) dependence similar to that of the BCS theory. A pseudogap evolves below 150 K, where the c-axis resistivity ρ_c is semiconducting. The normal-state tunneling resistance R_N shows a linear T dependence down to T_cexhibits an abrupt decrease at T_cand saturates at low T. This reflects scattering arising from an electronic interaction that is relevant to the high- T_c superconductivity.